Abstract: A wheelchair structure for preventing pressure ulcers is disclosed. A lifting mechanism is mounted under a seat cushion of a wheelchair, and a knee support is disposed on the front of a seat cushion. When the lifting mechanism lifts the seat cushion, proximal ends of tibias of a user can just lean on the knee support, and a foot pedal of the wheelchair can make the user have a posture with bent knees and in a shape of “<”, so that the user can change a sitting posture to prevent pressure ulcers caused by long-term pressure on the buttocks when sitting in the wheelchair.